1. Field of the Invention
The present invention relates to a calender for a sheet material, e.g., paper, cardboard, film, and other similar sheet material, including at least two successive treatment stations through which the sheet material passes. To influence predetermined parameters of the sheet material, each treatment station includes a plurality of adjacently positioned adjustment zones at a predetermined spacing to form a row laterally extending across the sheet material substantially perpendicular to the travel direction of the sheet material. The adjustment zones of one treatment station may be offset with respect to the adjustment zones of the other treatment station.
The term "calender" as used herein may encompass roll devices for processing sheet materials, e.g., paper, cardboard, film, and other similar material. The processing may include, e.g., refining the sheet material with regard to thickness, gloss, smoothness, and other properties. Therefore, calender, in accordance with the present invention, may encompass compact calenders and super calenders that have "soft" work gaps, which may be defined on one side by a hard roll and on an other side by a roll provided with an elastic cover, and also may encompass smoothing calenders whose work gaps are defined on both sides by hard rollers.
2. Discussion of the Background Information
A calender generally related to the calender discussed above has been disclosed, e.g., in the pamphlet from Voith Sulzer Papiertechnik entitled "Die Neue Softkalander-Generation" [The New Generation of Soft-Calenders], published in November 1994. According to this pamphlet, a paper sheet is conducted through two work gaps, each work gap formed between a hard roll and a roll provided with an elastic cover. The elastic roll is a deflection adjustment roll with a multitude of adjusting members positioned adjacent to one another as support elements for the elastic roll cover. Each adjusting member exerts a predetermined pressure to the inside of the elastic cover against a driven hard roll.
Given the above-noted arrangement, several problems and drawbacks may occur. For example, for technological reasons, a width of individual zones, i.e., a predefined zone generally including one or more adjusting members actuated by a single control signal, should be as small as possible so that narrow regions of influence are produced and narrow width defects in the profile can be corrected. However, notwithstanding whether the zones include one adjusting member or a number of adjusting members, as the zones become narrower, the structural expenditure and the production costs become greater. Moreover, certain adjusting members, e.g., hydrostatic support elements, cannot be produced any smaller than a predetermined width.